The engine cover is just a cover and tells you nothing. Even if he replaced the engine with a series III, he probably didn't replace the engine cover...
The L67 has a gen 3 5 rib supercharger and the L32 has a gen V 7 rib supercharger.
Both series II and III blocks are stamped, however a lot of series III engines use series II stamped blocks.
If it has black valve covers, it is most likely an L32 (although not all L32s had black valve covers).